Friday, November 10, 2006

Proof now established of the direct computation of optical flow fields between two hemispheres in the visual centre of flies:

For the first time, scientists at the Max Planck Institute for Neurobiology in Martinsried near Munich have been able to show how two nerve cells communicate with each other from different hemispheres in the visual centre. This astoundingly simple circuit diagram could at a later date provide a model for algorithms to be deployed in technical systems.

Movements in space create in humans and animals so-called optical flow fields which are characteristic for the movement in question. In a forward movement, the objects flow by laterally, objects at the front increase in size and objects further away hardly change at all. At a higher level in the visual centre in the brain, there must be a computation of the visual information, so that animals can differentiate between their own movement and movement of their environment and are able to correct their course if necessary. It is important for the analysis of flow fields that the movement information from both eyes is merged so that the whole flow field can be assessed. In their current study, Karl Farrow, Jürgen Haag and Alexander Borst have for the first time proved the direct link between two nerve cells, one in each half of the brain, combining the movement signals from both the facetted eyes of a fly.

Based on the journal Nature Neuroscience paper "Nonlinear, binocular interactions underlying flow field selectivity of a motion-sensitive neuron" (Abstract - Full text is currently available but this may change).

Books on Neuroscience from the Science and Evolution Bookshop: UK | US

From The Jerusalem Post: In the Jewish community, a curious feature of the controversy about Darwin and Intelligent Design is the funny way it has of making strange bedfellows. You might expect to find all religious conservatives lining up against Darwinism. Not so.

Darwinian theory asserts that an unguided and purely material process alone (natural selection) was sufficient to produce the whole history of life on earth.

Biblical religion, if it means anything at all, has to stand for the belief that life's history was guided in some way by a transcendent intelligence. You can't have an unguided guided process.

Yet more than a few people on the traditional side of the religious divide are vocal critics of intelligent design (ID), the scientific framework in which doubts about Darwinism are currently being expressed and worked out.

Much of the intellectual energy behind ID has been supplied by the Discovery Institute, where I work, here in Seattle.

So I was intrigued by the current issue of the Orthodox Union's magazine, Jewish Action, which includes a package of three articles on intelligent design.

Thursday, November 09, 2006

Jeffrey Meldrum (homepage) holds a Ph.D. in anatomical sciences and is a tenured professor of anatomy at Idaho State University. He is also one of the world's foremost authorities on Bigfoot (info), the mythical smelly ape-man of the Northwest woods. And Meldrum firmly believes the lumbering, shaggy brute exists.

That makes him an outcast - a solitary, Sasquatch-like figure himself - on the 12,700-student campus, where many scientists are embarrassed by what they call Meldrum's "pseudo-academic" pursuits and have called on the university to review his work with an eye toward revoking his tenure. One physics professor, D.P. Wells, wonders whether Meldrum plans to research Santa Claus, too.

Meldrum, 48, spends most of his days in his laboratory in the Life Sciences Building, analyzing more than 200 jumbo plaster casts of what he contends are Bigfoot footprints.

For the past 10 years, he has added his scholarly sounding research to a field full of sham videos and supermarket tabloid exposes. And he is convinced he has produced a body of evidence that proves there is a Bigfoot.

Videos of the "Patterson footage" (original plus 'shake-free' version) can be seen here. The page also contains links to other Bigfoot videos including one in which Meldrum discusses the Patterson tape. [Video]

From Nature journal: Using a technique that may one day help blind people to see, researchers have shown in mice that retinal cells from newborns transplanted into the eyes of blind adults wire up correctly and help them to detect light.

The finding challenges conventional biological thinking, because it shows that cells that have stopped dividing are better for transplantation than the stem cells that normally make new cells.

For decades, researchers have sought a way to replace the light-detecting cells that carpet the back of our eyes - and which break down in diseases such as retinitis pigmentosa and macular degeneration. But they have struggled to find cells that will work normally after being transplanted into the eye. [More]

Photoreceptor loss causes irreversible blindness in many retinal diseases. Repair of such damage by cell transplantation is one of the most feasible types of central nervous system repair; photoreceptor degeneration initially leaves the inner retinal circuitry intact and new photoreceptors need only make single, short synaptic connections to contribute to the retinotopic map. So far, brain- and retina-derived stem cells transplanted into adult retina have shown little evidence of being able to integrate into the outer nuclear layer and differentiate into new photoreceptors1, 2, 3, 4. Furthermore, there has been no demonstration that transplanted cells form functional synaptic connections with other neurons in the recipient retina or restore visual function. This might be because the mature mammalian retina lacks the ability to accept and incorporate stem cells or to promote photoreceptor differentiation. We hypothesized that committed progenitor or precursor cells at later ontogenetic stages might have a higher probability of success upon transplantation. Here we show that donor cells can integrate into the adult or degenerating retina if they are taken from the developing retina at a time coincident with the peak of rod genesis5. These transplanted cells integrate, differentiate into rod photoreceptors, form synaptic connections and improve visual function. Furthermore, we use genetically tagged post-mitotic rod precursors expressing the transcription factor Nrl (ref. 6) (neural retina leucine zipper) to show that successfully integrated rod photoreceptors are derived only from immature post-mitotic rod precursors and not from proliferating progenitor or stem cells. These findings define the ontogenetic stage of donor cells for successful rod photoreceptor transplantation.

From the Smithsonian: "To better understand bonobo intelligence, I traveled to Des Moines, Iowa, to meet Kanzi (info), a 26-year-old male bonobo reputedly able to converse with humans. When Kanzi was an infant, American psychologist Sue Savage-Rumbaugh tried to teach his mother, Matata, to communicate using a keyboard labeled with geometric symbols. Matata never really got the hang of it, but Kanzi - who usually played in the background, seemingly oblivious, during his mother's teaching sessions - picked up the language.

Kanzi learned to combine these symbols in regular ways, or in what linguists call 'proto-grammar'. Once, Savage-Rumbaugh says, on an outing in a forest by the Georgia State University laboratory where he was raised, Kanzi touched the symbols for'marshmallow'and 'fire'. Given matches and marshmallows, Kanzi snapped twigs for a fire, lit them with the matches and toasted the marshmallows on a stick.

News from the journal Science: Intelligent design (ID) received a drubbing yesterday, with pro-evolution candidates taking control of the Kansas State Board of Education and strengthening their representation on the Ohio State Board of Education. Many scientists also cheered the defeat of Senator Rick Santorum (R-PA), one of the most politically influential supporters of the ID movement.

In Ohio, incumbent board member Deborah Owens Fink lost decisively to Tom Sawyer, a former teacher and U.S. representative. Owens Fink had repeatedly attempted to dilute evolution in Ohio's science standards. Sawyer, who contested the seat at the urging of Ohio scientists, will help swell the ranks of moderates on the 19-member board. The scientists' group, Help Ohio Public Education, is also celebrating the victory of three other 'pro-science' candidates including incumbent G. R. 'Sam' Schloemer, who had described his candidacy as a referendum on ID. Schloemer won by a 2-to-1 margin over John Hritz, an ID supporter. The only pro-ID candidate elected Tuesday was Susan Haverkos.

In Kansas, supporters of evolution were already assured a majority on the 10-member state board after a primary election earlier this year.

Wednesday, November 08, 2006

Scientists are reconstructing the genome of Neanderthals - the close relations of modern man.

The ambitious project involves isolating genetic fragments from fossils of the prehistoric beings who originally inhabited Europe to map their complete DNA.

The Neanderthal people (info) were believed to have died out about 35,000 years ago - at a time when modern humans were advancing across the continent.

Lead researcher Dr Svante Paabo (homepage), an evolutionary geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, said: 'This would be the first time we have sequenced the entire genome of an extinct organism.'

...But the prospect of the genome providing the blueprint for resurrecting a living "Jurassic-Park-style" Neanderthal is unlikely.

From BBC News: UK scientists are seeking permission to place human nuclei into animal eggs in a bid to create stem cell lines.

Why do researchers believe the intermingling of species could be vital to science?

The mixing up and merging of species is not new to science: a multitude of creatures straddling the line between animal and human already exist in laboratories around the world.

But far from seeing their role as creators of freak-show fodder, scientists believe the creation of part-human part-animal creatures can help to study disease, advance areas such as fertility, and boost understanding of our basic biology.

These creatures are called chimeras (info), and are defined as organisms that contain at least two genetically different groups of cells originating from different organisms.

Did Interbreeding Between Humans and Neanderthals Lead to a Bigger Human Brain?

Might mating between an ancient human and a Neanderthal - perhaps occurring in only a single instance - have introduced a gene variant into the human population that enhanced human brain function? That question is at the heart of a new study by researchers at the Howard Hughes Medical Institute and the University of Chicago.

The scientists said they have developed the most robust genetic evidence to date that suggests humans and Neanderthals interbred when they existed together thousands of years ago. The interbreeding hypothesis contrasts with at least one prominent theory that posits that no interbreeding occurred when the two species encountered one another.

Lahn collaborated on the studies with Patrick D. Evans, Nitzan Mekel-Bobrov, Eric J. Vallender and Richard R. Hudson, all of the University of Chicago.

In their studies, Lahn and his colleagues performed a detailed statistical analysis of the DNA sequence structure of the gene microcephalin, which is known to play a role in regulating brain size in humans. Mutations in the human gene cause development of a much smaller brain, a condition called microcephaly.

Earlier studies by Lahn's group yielded evidence that the microcephalin gene has two distinct classes of alleles. One class, called the D alleles, is comprised of a group of alleles with rather similar DNA sequences. The other class is called the non-D alleles. Lahn and colleagues previously showed that all modern copies of the D alleles arose from a single progenitor copy about 37,000 years ago, which then increased in frequency rapidly and are now present in about 70 percent of the world's population. This rapid rise in frequency indicates that the D alleles underwent positive selection in the recent history of humans. This means that these alleles conferred a fitness advantage on those who possessed one of them such that these people had slightly higher reproductive success than people who didn't possess the alleles, said Lahn.

The estimate that all modern copies of the D alleles descended from a single progenitor copy about 37,000 years ago is based on the measurement of sequence difference between different copies of the D alleles. As a copy of a gene is passed from one generation to the next, mutations are introduced at a steady rate, such that a certain number of generations later, the descendent copies of the gene would on average vary from one another in DNA sequence by a certain amount. The greater the number of the generations, the more DNA sequence difference there would be between two descendent copies, said Lahn. The amount of sequence difference between different copies of a gene can therefore be used to estimate the amount of evolutionary time that has elapsed since the two copies descended from their common progenitor.

In the new studies reported in PNAS, the researchers performed detailed sequence comparisons between the D alleles and the non-D alleles of microcephalin. The scientists determined that these two classes of alleles have likely evolved in two separate lineages for about 1.1 million years - with the non-D alleles having evolved in the Homo sapiens lineage and the D alleles having evolved in an archaic, and now extinct, Homo lineage. Then, about 37,000 years ago, a copy of the D allele crossed from the archaic Homo lineage into humans, possibly by interbreeding between members of the two populations. This copy subsequently spread in humans from a single copy when it first crossed into humans to an allele that is now present in an estimated 70 percent of the population worldwide today.

The estimate of 1.1 million years that separates the two lineages is based on the amount of sequence difference between the D and the non-D alleles. Although the identity of this archaic Homo lineage is yet to be determined, the researchers argue that a likely candidate is the Neanderthals. The 1.1 million year separation between humans and this archaic Homo species is roughly consistent with previous estimates of the amount of evolutionary time separating the Homo sapiens lineage and the Neanderthal lineage, said Lahn. Furthermore, the time of introgression of the D allele into humans - about 37,000 years ago - is when humans and Neanderthals coexisted in many parts of the world.

Lahn said the group's data suggest that the interbreeding was unlikely to be a thorough genetic mixing, but rather a rare - and perhaps even a single - event that introduced the ancestral D allele previously present in this other Homo species into the human line.

"By no means do these findings constitute definitive proof that a Neanderthal was the source of the original copy of the D allele," said Lahn. "However, our evidence shows that it is one of the best candidates. The timeline - including the introgression of the allele into humans 37,000 years ago and its origin in a lineage that separated with the human line 1.1 million years ago - agrees with the contact between, and the evolutionary history of, Neanderthals and humans.

"And a third line of evidence, albeit weaker, is that the D alleles are much more prevalent in Eurasia and lower in sub-Saharan Africa, which is consistent with an origin in the former area. And we know that Neanderthals evolved outside of Africa," said Lahn.

Lahn also said that although the disruption of the microcephalin gene in humans leads to smaller brains, the role of the D alleles in brain evolution remains unknown. "The D alleles may not even change brain size; they may only make the brain a bit more efficient if it indeed affects brain function," he said. "For example, someone inheriting the D allele may have only a slightly more efficient brain on average. While that enhancement might confer only a subtle evolutionary advantage on that person, when that effect is propagated over a thousand generations of natural selection, the result will be to drive the D alleles to a very high prevalence."

Lahn and his colleagues believe that other genes might well show similar telltale signs of an origin in archaic Homo lineages such as Neanderthals. They are currently using their analytical tool to search for evidence of that origin for other genes in the human genome.

Such findings may have broader implications for understanding human evolution than just revealing the possibility of human-Neanderthal interbreeding, he said. "In addition to being perhaps the most robust genetic evidence for introgression of genes from archaic Homo species into humans, I think this finding demonstrates that the evolution of our species has been profoundly impacted by gene flow from our relative species," said Lahn.

"Finding evidence of mixing is not all that surprising. But our study demonstrates the possibility that interbreeding contributed advantageous variants into the human gene pool that subsequently spread. This implies that the evolution of human biology has been affected by the contribution of advantageous genetic variants from archaic relatives that we have replaced or even killed off," he said.

Until now, said Lahn, the scientific debate over genetic exchange between humans and other Homo species has led to two prominent competing theories. One holds that anatomically modern humans replaced archaic species, with no interbreeding. And the other states that extensive interbreeding did take place and that modern humans evolved from that interbreeding in many regions of the world.

Genetic and fossil evidence for the latter "multiregional" theory has been inconclusive, said Lahn, so that theory has been largely discredited. However, he said, the newer evidence of gene exchange - as well as other genetic evidence that might follow - could give rise to a more moderate version holding that some genetic exchange did take place. Furthermore, it will become increasingly appreciated that such genetic exchange might have made our species much more fit.

At the center of the debate on the emergence of modern humans and their spread throughout the globe is the question of whether archaic Homo lineages contributed to the modern human gene pool, and more importantly, whether such contributions impacted the evolutionary adaptation of our species. A major obstacle to answering this question is that low levels of admixture with archaic lineages are not expected to leave extensive traces in the modern human gene pool because of genetic drift. Loci that have undergone strong positive selection, however, offer a unique opportunity to identify low-level admixture with archaic lineages, provided that the introgressed archaic allele has risen to high frequency under positive selection. The gene microcephalin (MCPH1) regulates brain size during development and has experienced positive selection in the lineage leading to Homo sapiens. Within modern humans, a group of closely related haplotypes at this locus, known as haplogroup D, rose from a single copy {approx}37,000 years ago and swept to exceptionally high frequency ({approx}70% worldwide today) because of positive selection. Here, we examine the origin of haplogroup D. By using the interhaplogroup divergence test, we show that haplogroup D likely originated from a lineage separated from modern humans {approx}1.1 million years ago and introgressed into humans by {approx}37,000 years ago. This finding supports the possibility of admixture between modern humans and archaic Homo populations (Neanderthals being one possibility). Furthermore, it buttresses the important notion that, through such adminture, our species has benefited evolutionarily by gaining new advantageous alleles. The interhaplogroup divergence test developed here may be broadly applicable to the detection of introgression at other loci in the human genome or in genomes of other species.

Tuesday, November 07, 2006

A 'spectacular beast' is coming back to its original stomping grounds and making a new home at the University of Alberta - a coup that will allow its researchers to study the rare dinosaur skull up close.

'This is a very dramatic beast,' said Dr. Michael Caldwell (homepage), a palaeontolgist who was instrumental in getting the skull to the U of A. 'What we will have is a cast, but the specimen is one of a kind in the world. This is the last cast from the original mould and when you have a research quality cast where it is duplicated right down to a freckle, it doesn't get any better than that.'

The fossils from this large herbivorous dinosaur were first found by the Sternberg family, who were hired by the Geological Survey of Canada to compete with Americans coming to Alberta to collect fossils. The Sternbergs gathered all kinds of bones, including the skull of Styracosaurus albertensis (info). 'The specimen was perfect,' says Caldwell. 'And it's a big one - the skull is two metres long.'

From Proceedings of the National Academy of Sciences (PNAS) 'Early Edition' information:

Re-evaluating Ant Evolution and Diversity - "As highly social organisms, ants display advanced social adaptations within their ranks, such as agriculture, herding, and enslavement. Ant species are widespread globally, but how ants evolved to their present-day dominance remains unresolved because fossil, molecular, and morphological data seem to provide conflicting answers. To address this issue, Sean Brady et al. generated and analyzed reportedly the most comprehensive molecular phylogenetic data set assembled to date for ants; the sequences encompass 151 species in all 20 living subfamilies, as well as 11 outgroup species from related aculeate wasp families. Different methods of analysis yielded different tree topologies, illustrating how inferences about ant relationships are sensitive to methods and assumptions. The results demonstrate that recent hypotheses, such as the existence of a poneroid clade or that the subfamily Leptanillinae is sister to the rest of the ants, may not be certain. Brady et al. also estimate that the last common ancestor of extant ants existed ~115-135 million years ago, within the time frame of 120 million years ago suggested by the fossil record." [Myrmecology, Morphology, Phylogeny, Topology, DNA]-------

Based on "Evaluating alternative hypotheses for the early evolution and diversification of ants" (Abstract)

Entomology: Books on 'Insects and Evolution' from the Science and Evolution Bookshop: UK | US

"On this episode of Intelligent Design The Future CSC's Logan Gage asks, who wrote Richard Dawkins' latest book, The God Delusion (Amazon UK | US)? Gage interviews AEI's Joe Manzari who questioned Dawkins about this at a recent event promoting the book. A strong determinist, which Dawkins would seem to be as a staunchly atheistic Darwinist, believes that everything is pre-determined by material processes. So, taking c.redit for writing a book is illogical. Does Dawkins believe determinism is true? Does he think people are responsible for their actions or not?" [Center for Science and Culture, Evolution, Podcast, ID]

Listen to "Is Richard Dawkins Contradicting Himself by Taking Credit for Writing His Own Book?" here (and view the archives).

From the Houston Chronicle, Texas: East Montgomery County could become home to a dinosaur theme park complete with dinosaur skeletons, animals and mock fossil digs, park developers announced Thursday.

The Pennsylvania-based Exhibits Rex plans to open Dinosaur City in 2008, but there are a lot of details to be worked out first.

The company and the East Montgomery County Improvement District hope to complete a deal next week that would require the district to find a 100-acre site next to U.S. 59 and get Legislative approval for a special economic zone and half-penny sales tax increase to repay about $25 million in revenue bonds."

"'Dino' Don Lessem is the leading presenter of dinosaur science. Author of more than twenty books, advisor to Jurassic Park and Disney Dinosaur films, host and author of NOVA and Discovery Channel films, Mr. Lessem has spent the last 15 years traveling the world in search of dinosaurs, from Mongolia to Arctic Alaska."-------

Monday, November 06, 2006

From USA Today: Vatican City (AP) - Scientists advising Pope Benedict XVI told the pontiff on Monday that they will study scientific insights into evolution, reflecting his special interest in the subject.

No date has been set for the meeting exploring 'scientific insights into the evolution of the universe and of life,' which Cabibbo noted was of 'special interest' to the pope. Generally, the plenary session of the academy meets every two years.

Benedict's predecessor, John Paul II, told the academy in 1996 that Charles Darwin's theories on evolution were sound as long as they took into account that creation was the work of God and that Darwin's theory of evolution was 'more than a hypothesis.'"

Complete online text of Pope Benedict XVI address to the plenary assembly of the Papal Academy of Sciences: "Il testo integrale del discorso del papa in lingua inglese" ("The integral text of the speech of the Pope in English language" - only the first paragraph is in italian) [Joseph Alois Ratzinger]

Explore the changing physiology of our ancestors and discover the unique physical traits that define us as humans.

Lineages:

Humans are the only surviving branch of a diverse family tree. Follow the evolutionary journeys of our ancestors.

Culture:

Discover how an advanced culture helps humans understand ourselves, each other, and our place in the natural world.-------

*Biography: "Dr. Donald Johanson is one of the world's leading and America's best known paleoanthropologists. Working in Africa, he has dedicated the last twenty-five years to exploring, discovering and studying the most significant fossil finds ever made in the se arch for our origins.

His dramatic discovery, in 1974, of LUCY our oldest, most complete human ancestor sparked a controversial change in our view of human origins. The following year, again at the famous site of Hadar, Ethiopia, Johanson's team made the unprecedented discover y of the fossilized remains of some 13 individuals. Believed to be the oldest evidence of human ancestors living in groups, the National Geographic Society dubbed the fossils the First Family."

'...How hard it is for those who have riches to enter into the Kingdom of God! For it is easier for a camel to enter in through a needle's eye, than for a rich man to enter into the Kingdom of God.' - Luke 18: 24-25

Pensacola evangelist and tax protester Kent Hovind winked at his wife and gave her a reassuring smile as he was led away to jail.

Jo Hovind clutched the necktie he had been wearing. She kept her eyes on her husband until he was out of sight.

A 12-person jury deliberated for 21/2 hours on Thursday before finding the couple guilty of all counts in their tax-fraud case.

From University at Buffalo Campus News: In the ongoing debate of intelligent design versus scientific evolution, film writer and director Randy Olson set out to find which side's advocates can't take flight.

His film, 'Flock of Dodos,' was screened on campus last week, followed by a six-member panel discussion on Friday in Park Hall.

...Explaining creationism, the film uses imagery including a wall with holes in it - according to creationists in the film, the holes represent the unexplained and are filled by God.

Some, however, refuse to give up on finding answers to those questions.

Sunday, November 05, 2006

Neuron Cell Stickiness May Hold Key To Evolution Of The Human Brain

The stickiness of human neurons may have been a key factor in why the human brain evolved beyond the brains of our primate relatives.

In a study comparing the genomes of humans, chimpanzees, mice and other vertebrates, researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and Joint Genome Institute (JGI) found a strikingly high degree of genetic differences in DNA sequences that appear to regulate genes involved in nerve cell adhesion molecules. Cell adhesion controls many aspects of brain development including growth and structure, and enables neurons to connect with other neurons and supportive proteins. Differences in the molecular connections of human neurons compared to the neurons of chimps, mice and other animals, could help explain why the human brain is capable of far more complex cognitive functions.

In a paper published in the November 3, 2006 issue of the journal Science, a team of researchers led by Edward Rubin, MD, director of both JGI and Berkeley Lab's Genomics Division, report on a comparative genomics study of conserved noncoding sequences (CNSs) - sequences of DNA shared by many different organisms that do not code for proteins but play an important role in regulating gene expression. In their Science paper, the researchers identified 992 CNSs whose sequences were specifically modified in humans and enriched near genes involved in neuronal cell adhesion. This is the first genome-wide unbiased study to detect clear evidence of human-specific evolution in brain-related sequences. After further comparisons, the researchers concluded these CNSs "may have contributed to the uniquely human features of brain development and function."

"One of the big questions in genetics is what are the DNA sequences in the human genome responsible for the capabilities that distinguish us from the rest of the animal kingdom," said Rubin. "We have long suspected that it would be a combination of DNA sequences coding for genes and DNA sequences that control when genes are switched on or off. In this study by comparing the entire genome of many organisms to that of humans we were able to identify a series of human-specific sequence changes that have a high likelihood of turning genes on and off."

Homo sapiens share more than 98 percent of their genome with their chimpanzee cousins, but the final products of those genomes are quite dissimilar. Nowhere are these differences more pronounced than in the brain, where the human model is far larger and more complex than those of all other primates. Previous unbiased whole-genome studies that focused on genes have failed to find a broad pattern of human-specific evolution in brain genes. This led the Berkeley Lab researchers to suspect that the genetic basis of human-specific brain evolution might be found in the sequences that regulate genes, rather than the genes themselves.

Rubin is a leading authority on CNSs who has advanced the principle that if evolution has conserved a specific non-coding DNA sequence over many millions of years, the sequence is likely to function as a switch turning genes on or off. In this latest study, he and his Science co-authors investigated whether CNSs also bear the signature of accelerated evolution.

Explained Prabhakar, who devised the statistical methods and performed most of the computational analysis for this study, "We started with a set of 110,549 CNSs previously identified by whole-genome multiple sequence comparisons and known to have evolved over at least the last 100 million years. We measured the average rate of evolution in the human lineage in these sequences and then identified 992 elements with a significant excess of human-specific nucleotide substitutions relative to the baseline. This is about 79-percent more than we would expect to see by chance at our assigned probability threshold."

When Prabhakar and Noonan ran an analysis to determine whether the accelerated CNSs disproportionately occurred near genes with particular functions, they discovered that neuronal cell adhesion was the only biological process displaying a significant excess of accelerated CNSs. To determine whether this pattern of accelerated CNSs was repeated in other animals, the researchers performed similar analyses on the chimpanzee and mouse genomes. They examined 1,050 accelerated chimpanzee CNSs and 4,707 accelerated mouse CNSs.

Said Noonan, "While the accelerated chimpanzee CNSs were also significantly enriched near neuronal cell adhesion genes, there was no overlap between them and human DNA sequences, which suggests that the accelerated evolution of adhesion cell function occurred independently in humans and chimpanzees. We failed to detect any CNS enrichment near cell adhesion genes in mice."

The actual differences in the distribution of neuronal adhesion proteins in human versus chimpanzee brains are currently not known, but the Berkeley Lab-JGI researchers are now conducting experiments to determine the functional consequences of the accelerated CNSs they've identified.

Said Prabhakar, "On the computational side, we're trying to identify other kinds of sequence changes that may have played a role in human evolution, such as nucleotide insertions, deletions or duplications, and chromosomal rearrangements."

Added Rubin, "In hindsight the results of our study make sense since our cognitive abilities are clearly one of the most distinct of all human attributes and we would expect these abilities to result from human-specific aspects of neuronal development. Our results also suggest that analysis of the differences in human and chimpanzee neuronal cell adhesion gene expression is a good place to begin exploring the molecular basis of how humans became so cognitively advanced in the 5 to 6 million years since we shared a common ancestor with chimps."

This research was supported by grants from the U.S. Department of Energy, the National Heart, Lung and Blood Institute and the National Institute of General Medical Sciences.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California. Visit our Website at www.lbl.gov/

Changes in gene regulation likely influenced the profound phenotypic divergence of humans from other mammals, but the extent of adaptive substitution in human regulatory sequences remains unknown. We identified 992 conserved noncoding sequences (CNSs) with a significant excess of human-specific substitutions. These accelerated elements were disproportionately found near genes involved in neuronal cell adhesion. To assess the uniqueness of human noncoding evolution, we examined CNSs accelerated in chimpanzee and mouse. Although we observed a similar enrichment near neuronal adhesion genes in chimpanzee, the accelerated CNSs themselves exhibited almost no overlap with those in human, suggesting independent evolution toward different neuronal phenotypes in each species. CNSs accelerated in mouse showed no bias toward neuronal cell adhesion. Our results indicate that widespread cis-regulatory changes in human evolution may have contributed to uniquely human features of brain development and function.